The overall objective of this project is twofold: 1) To add to the newly forming body of knowledge establishing the rat as a useful animal model by which to study the neurophysiological, nutritional and behavioral processes of aging. 2) To contribute to the development of an objective neurophysiological technique which will facilitate the understanding of the aging process and its associated physiological, behavioral and environmental facets. The primary objective of the investigation is to determine the extent to which the visual evoked potential (VEP) is altered in the aging rat. Possible contributing factors, such as sensory receptor and central nervous system deterioration, are also considered. This will be accomplished by recording VEP's in 2, 12, and 26 month old rats with chronical implanted bilateral electrodes in the lateral geniculate nucleus and visual cortex. VEP responses in both lightly anesthetized and unanesthetized animals will be recorded twice to determine reliability. Two experiments will be performed, one involving peripheral stimulation using single and double photic flashes, the other involving central electrical stimulation delivered through an additional electrode implanted in the optic nerve. Ten subjects will be used in each age group for each experiment. VEP's will be computer analyzed for amplitude and latency changes. Histological examination will verify electrode placement and look for degenerative changes in the aging brain.